package sort;

/**
 * @author czt
 * @version 1.0
 * @since 2025/1/9
 * 归并排序
 */
public class Merge {

    public static void merge(int[] a1, int i, int iEnd, int j, int jEnd, int[] a2) {
        int k = 0;
        while (i <= iEnd && j <= jEnd) {
            if (a1[i] < a1[j]) {
                a2[k] = a1[i];
                i++;
            } else {
                a2[k] = a1[j];
                j++;
            }
            k++;
        }
        if (i > iEnd) {
            System.arraycopy(a1, j, a2, k , jEnd - j + 1);
        }
        if (j > jEnd) {
            System.arraycopy(a1, i, a2, k, iEnd - i + 1);
        }
    }

    public static void sort(int[] a1) {
        int[] a2 = new int[a1.length];
        split(a1, 0, a1.length - 1,a2);
    }

    private static void split(int[] a1, int left, int right, int[] a2) {
        // 2.治
        if (left == right) {
            return;
        }
        // 1.分
        int m = (left + right) >>> 1;
        split(a1, left, m,a2);
        split(a1, m + 1, right,a2);
        // 3.合
        merge(a1, left, m, m + 1, right, a2);
        System.arraycopy(a2, left, a1, left, right - left + 1);
    }
}
